1. Field of the Invention
The present invention relates to a method for recovering valuable metals from a spent lithium ion secondary battery, and wastes (for example, a cathode active material) generated in the method for producing a lithium ion secondary battery. More specifically, the invention relates to a method for extracting nickel and lithium from a solution generated when a cathode material of a lithium ion secondary battery is treated by extraction with a solvent, concentrating the solution into which lithium and nickel are extracted, separating nickel and lithium from each other by use of another solvent, and then recovering nickel in the form of nickel carbonate or nickel powder, and lithium in the form of lithium carbonate.
2. Description of the Related Art
The use manners of a lithium ion secondary battery have been rapidly spreading, and the production quantity thereof is expected to increase rapidly. In a lithium ion secondary battery, relatively expensive metals such as cobalt and nickel are used; however, under the present circumstance, it is not difficult to say that the process for recovering the metals has been established. It is evident that as the production quantity increases, the generation amount of spent lithium ion batteries, and that of cathode active materials and others that are discarded by the generation of defects in the production process and other causes also increase. Thus, it is important to recover manganese, cobalt, nickel, and lithium.
A process for recovering manganese, cobalt, nickel and lithium from spent lithium ion secondary batteries is disclosed in the Japanese Patent Application Laid-Open No. 2007-122885 (Patent Document 1). According to this process, cobalt and nickel cannot be effectively separated from each other. Unless cobalt- and nickel-refining steps and so on are separately carried out, cobalt and nickel cannot be individually recovered.
As a process for recovering cobalt, nickel and lithium, there has been known a solvent extraction process as disclosed in Japanese Patent Application Laid-Open No. 2008-231522 (Patent Document 2). This process is characterized in that even in a case where manganese is contained in a spent lithium ion secondary battery to which the process is to be applied, the process can cope with this case. However, in order to generate lithium carbonate from a solution remaining after cobalt, nickel and manganese are recovered, some operation for concentrating lithium is required when the concentration of lithium is small.
In the meantime, a process for recovering lithium from a lithium solution by solvent extraction has been also known. As disclosed in Japanese Patent Application Laid-Open No. 2006-57142 (Patent Document 3), in the case of making an attempt for recovering lithium in the form of a carbonate thereof, it is generally difficult to recover the carbonate from a thin solution of lithium. It is essential to concentrate the lithium solution by some method. As a method therefor, solvent extraction has been adopted in the Patent Document 3. This process makes it possible to recover only lithium, and may result in a high cost performance in the light of the price of lithium carbonate.
Japanese Patent Application Laid-Open No. 2004-307983 (Patent Document 4) discloses a β-hydrooxime type extractant (for example, trade name: LIX-841, manufactured by Cognis Co.) as a nickel-extracting agent. According to this extractant, lithium is hardly extracted when nickel is extracted; therefore, the extractant has an advantage that the performance of separating nickel and lithium from each other is high. However, it is necessary for a practical use thereof to improve the performance for back-extracting nickel. Moreover, according to this extractant, lithium cannot be concentrated although nickel can be concentrated. When the concentration of lithium is small in a solution from which nickel has been extracted, lithium cannot be recovered in the form of lithium carbonate unless lithium is concentrated.
In electrolytic recovery of nickel, it is generally necessary that the concentration of nickel in an electrolytic solution is about 50 g/L. From a solution having a concentration smaller than this concentration, an effective electrolytic recovery cannot be attained. Thus, about a solution having a small nickel concentration, it is necessary to increase the nickel concentration by some method. It is supposed to use, as the method for increasing the nickel concentration, a method for adding a carbonating agent and an alkaline agent to a solution having a small nickel concentration to precipitate nickel, and then dissolving this precipitation again, thereby yielding a solution having a required nickel concentration. However, according to this method, it is necessary to conduct a solid-liquid separating operation for recovering the precipitated nickel. Moreover, a neutralizing agent which cannot be recycled is also required.